PCI-PCI Bridges

[johnsa]

Hi,

I've finished all my PCI and PCIe support functions and i've created a small db of vendor/device id's. The bus enumeration is working well and I can see a list of all said devices with names/models from the DB.
What I wanted to double check on is that in some of the Linux docs they mention having to configure the PCI-PCI bridge devices to know subordinate bus/parent bus/max io/mem windows. Is this still necessary or doesn't the BIOS do this all for you?
Assuming you don't change any of the device's addresses (IE: remap them .. edit the BARs) then I guess it would be necessary to update the downstream bridges? - and initially I can't think why I'd want to change their mappings.

[Combuster]

Since devices don't generally work when behind a misconfigured bridge, the bios does that for you. However, bridges are practically always present in the chipset, so if you add a bridge as an external device, the bios may miss it because it has it all hardcoded...

[johnsa]

Thats a good point, I didn't think about hot-adding some extra device that would act as a pci bridge. Although off the top of my head I can't think what might do this? Possibly something more in a server environment or via one of the pci conversions to an external unit, like pci to pcmcia that has a bridge in it. Either way it's good to know and I think i can safely ignore it until i get much further. I'm not going to be hot-swapping anything for now or using pcmcia/external pci devices.

Thanks!